Devices for damping pressure surges include hydraulic accumulators. One of the main functions of hydraulic accumulators is to receive specified volumes of a pressurized fluid of a hydraulic system and to return them to the system as required. Since the fluid is pressurized, hydraulic accumulators are treated as pressure vessels and must be designed to withstand the maximum operating pressure as determined by the approval standard. For volume equalization in the hydraulic accumulator and as a result the associated storage of energy, the pressurized fluid in the hydraulic accumulator is subjected to the force exerted by a weight, spring, or gas. Equilibrium always prevails between the pressure of the pressurized fluid and the opposing pressure generated by the force of the spring or by the gas. In most hydraulic systems, use is made of hydropneumatic accumulators, that is, ones subjected to the action of a gas and having a separating element. A distinction is made between bladder, piston-type, and diaphragm accumulators.
These hydropneumatic accumulators perform a wide variety of functions in a hydraulic system. For example, in addition to performing the energy storage function referred to, they may be called upon to contribute to absorption of mechanical shocks and to surge damping in hydraulic systems. Pulsations occur in the flow volume especially when hydraulic pumps such as positive-displacement pumps are employed. Such pulsations cause vibrations as well as noise, and may result in damage to the hydraulic system as a whole.
The hydraulic pumps in question, positive-displacement pumps in particular, are also employed in so-called common-rail technology in the area of diesel engines. Recent third-generation developments add piezo technology for injection systems for diesel fuel. The recently developed piezo inline injectors for the third common-rail generation (cf. VDI-Nachrichten [Association of German Engineers-News], No. 33, Aug. 15, 2003) use piezo actor modules, which act by coupler modules on switching valves. The switching valves in turn act on an injector module of the fuel injection system. The outstanding hydraulic rapidity of the system results from the high degree of integration of the inline injector, that is, from the nearness of the piezo package to the valve needle in the tip of the injector. In comparison to the previous generation, the mass moved was reduced in the new systems from 16 g to 4 g. The mass moved is understood to mean the mass of the valve needle and the fuel with which the control space is filled. The respective technical configuration requires very high system pressures, ones reaching the order of magnitude of 2200 bar. The respective system pressure is to be built up by the hydraulic pump indicated, in particular a positive-displacement pump. The build-up is attended by the disadvantages described of pressure and pulsation surges. If the pressure surges are transmitted to the injector system, this transmission may result in critical states of the system and in failure of the piezo injector system with the injection system. If, as is known in the state of the art (see DE 195 39 885 A1), conventional hydraulic accumulators with separating elements (pistons) are included in the diesel fluid system as outlined in the foregoing. They nevertheless encounter their limits in view of the high system pressures indicated of up to 2200 bar.
DE 101 48 220 A1 discloses another device for damping pressure pulsations in a fluid system, especially in a fluid system of an internal combustion engine. The device disclosed comprises a housing in which at least one operating space is present. This space is connected to the fluid system and is limited in area by at least one movable wall element in the form of a metal diaphragm mounted on the edge side in the housing so as to be stationary. This wall element is functionally connected to a first spring unit. To provide the possibility of smoothing out pressure pulsations in the fluid system even with variable pressure present, provision is made such that the device comprises at least a second movable wall element which delimits a second operating space and which has a metal diaphragm fastened on the edge side in the housing. The first spring unit is mounted between the two wall elements in the form of diaphragms and is functionally connected to both. A throttle unit is also provided by which the second operating space is connected to the fluid system. The pressure pulsations in a fluid system may be reliably and efficiently smoothed out with different pressure levels present. However, because of the stationary clamping of the wall elements (diaphragms) their movability is restricted, so that functional safety in operation may be endangered at high pressures and correspondingly large pulsation and pressure surges.